(1.) Field of the Invention
The present invention relates to an expansion valve, and more particularly to an expansion valve that senses the temperature and pressure of refrigerant in an outlet of an evaporator in a refrigeration cycle for an automotive air conditioning system, and controls the amount of refrigerant to be supplied to the evaporator.
(2.) Description of the Related Art
In an automotive air conditioning system, a refrigeration cycle is formed such that high-temperature, high-pressure gaseous refrigerant compressed by a compressor is condensed by a condenser; the condensed refrigerant is caused to undergo gas/liquid separation by a receiver/dryer; liquid refrigerant obtained by the gas/liquid separation is caused to undergo adiabatic expansion by an expansion valve, to be changed into low-temperature, low-pressure refrigerant, which is then evaporated by an evaporator; and the evaporated refrigerant is returned to the compressor. The evaporator to which is supplied the low-pressure refrigerant exchanges heat with the air in the compartment, to thereby cool the same.
The expansion valve comprises a power element that has pressure therein increased and decreased by sensing changes in the temperature and pressure of refrigerant on the outlet side of the evaporator, and a valve portion that controls the amount of refrigerant to be supplied to the inlet side of the evaporator based on the increase and decrease in pressure within the power element.
The power element includes a temperature-sensing chamber partitioned by a diaphragm made of a thin metal plate. When the power element senses changes in the temperature and pressure of refrigerant, the pressure within the temperature-sensing chamber is changed to displace the diaphragm. The displacement of the diaphragm is transmitted to a valve element of the valve portion via a shaft that extends axially, to cause the valve portion to perform opening/closing operation, whereby the flow rate of refrigerant through the valve is controlled. The valve portion has a valve seat formed in a passage extending between a port to which high-pressure refrigerant is introduced and a port from which adiabatically-expanded low-pressure refrigerant is allowed to flow. The valve element is disposed such that it can move to and away from the valve seat on an upstream side where high-pressure refrigerant is received, and the valve element is driven for opening/closing operation by the shaft extending from the power element through the valve hole thereof.
The expansion valve constructed as above is disposed in an engine room, a compartment or a partition dividing them, and in the expansion valve, a pipe leading to the receiver/dryer is connected to the high-pressure inlet port of the valve portion, a pipe leading to the evaporator is connected to the low-pressure outlet port of the same, a pipe from the evaporator is connected to the low-pressure inlet port of the power element, and a pipe extending to the compressor is connected to the low-pressure outlet port of the same. In a general expansion valve, a low-pressure outlet port to which is connected a pipe extending to the compressor is provided in the same side surface where a high-pressure inlet port of a valve portion is formed, and in an opposite side surface to the side surface, there are provided a low-pressure outlet port of the valve portion and a low-pressure inlet port to which is connected a pipe from the evaporator. That is, the low-pressure outlet port though which refrigerant from the expansion valve is guided out is formed along an axis parallel to the axis of the high-pressure inlet port through which refrigerant is introduced to the expansion valve, while the low-pressure inlet and outlet ports for causing refrigerant returned from the evaporator to flow to the compressor are disposed on the same axis. This means that e.g. when the expansion valve and the evaporator are mounted in a narrow mounting space, such as an engine room, the flexibility in layout thereof is sometimes limited. For example, when the direction of a pipe of the expansion valve, connected to the evaporator, and the direction of pipes of the expansion valve, connected to the receiver/dryer and the compressor, are caused to be orthogonal to each other, the pipe connected to the compressor has to be bent halfway, which requires an extra space for bending the pipe.
To avoid this inconvenience, an expansion valve has been proposed which is configured to be capable of having pipes connected to a body block in the form of a prism at right angles (see e.g. Japanese Unexamined Patent Publication (Kokai) No. 2001-241808 (Paragraph No. [0024], and FIGS. 7 and 8)) by forming ports to which are connected the pipes, in two adjacent side surfaces of the body block. This expansion valve is configured such that the axis of the high-pressure inlet port of the valve portion and the axis of the low-pressure outlet port thereof are orthogonal to each other, and the axes of the low-pressure inlet port and the low-pressure outlet port through which refrigerant returned from the evaporator passes are orthogonal to each other. Due to this construction, since the four ports are provided in the two adjacent side surfaces of the body block, it becomes possible to efficiently accommodate the expansion valve within a limited space. Now, a description will be given of the construction of a low-pressure passage through which refrigerant returned from the evaporator passes to flow to the compressor.
FIG. 26 is a cross-sectional view of a low-pressure passage of a conventional expansion valve.
The conventional expansion valve includes a low-pressure inlet port 101 for introducing refrigerant returned from the evaporator and a low-pressure outlet port 102 for a pipe connected to the compressor, on respective two adjacent side surfaces of a body block 100 in the form of a prism, and a low-pressure passage 103 having portions that extend from the low-pressure inlet port 101 and the low-pressure outlet port 102 along their axes and intersect at right angles within the body block 100. The low-pressure passage 103 is formed by making holes with drills such that the respective axes of the holes are orthogonal to each other, and when forming the holes, they are drilled until the tip of one of the drills sufficiently passes through a hole made by the other of the drills, such that the holes formed by the respective drills positively communicate with each other within the body block 100.
As a result, when refrigerant introduced from the evaporator into the low-pressure inlet port 101 flows through the low-pressure passage 103, the direction of flow thereof is changed at right angles, whereafter it flows from the low-pressure outlet port 102 to the compressor. Since the expansion valve itself contains the refrigerant passage bent at right angles, there is no need to bend pipes connected to the expansion valve, thereby making it possible to arrange the piping over the shortest length.
However, when the low-pressure passage 103 is formed by drilling from the two adjacent side surfaces, drilling is continued until the tip of one drill positively passes through a portion of the cylindrical low-pressure passage 103 formed by the other drill in a direction orthogonal to the direction of drilling by the drill, and hence inner walls of the portions of the low-pressure passage 103 on the outer peripheral sides thereof, which are orthogonal to each other, are formed with recesses 104 and edge portions 105 by the tip and its vicinity of each drill. When refrigerant passes the recesses 104 and the edge portions 105 at a faster flow speed than it flows along the inner peripheral side of the low-pressure passage 103, the flow of refrigerant is made turbulent to generate unusual noise, and the turbulent flow of the refrigerant increases noise of the flow of refrigerant.